I. Field of the Invention
This invention pertains to a bench-scale flammability test apparatus and method for testing the flammability of a liquid or solid material.
II. Description of the Prior Art
There are a number of factors that determine the flammability of a material, many of which reflect the synergistic couplings between a burning fuel and its environment. These factors include (1) the imposed heat flux levels, (2) the geometric arrangement of the fuel, (3) the presence of other nearby materials and the nature of those fuels, and (4) the temperature, pressure and degree of vitiation of the surrounding atmosphere. In different situations, these factors can have a marked effect upon the flammability rankings of a material. In the prior art, flammability tests have attempted to take these factors into consideration, with varying degrees of success.
Unfortunately, many of the prior art material flammability tests available today attempt to infer large-scale flammability on the basis of bench-scale testing without properly taking into account an additional factor of great importance, that is, fire scale. It is now known that the relative flammability rankings of materials at small scale, such as that tested in a bench-scale apparatus, can be markedly different from the flammability rankings of those materials at large scale, due largely to the differences in burning mechanisms at small and large scales. One reason for the disparity between flammability characteristics at large and small scale is that, when a large amount of a fuel is pyrolized and burned, the flames are thicker and the radiative heat transfer from the flames can significantly increase the flammability hazards associated with the fuel. This radiation is generally unimportant at small scale, but dominant at large scale. Recent research has shown that the degree of radiation from various fuels at large scale is closely correlated with their sootiness, which is measured at small scale by the subject invention.
Heretofore, the test methods and apparatus of the prior art have attempted to remove the disparity between flammability measurements taken at bench scale and those taken at large scale by imposing an external radiant flux on the samples while measuring their heat release by combustion. Attempts are made thereby to infer large-scale flammability from these bench-scale tests. However, such methods and devices are inadequate for a number of important reasons. To begin with, they are typically cumbersome, require considerable chemical analysis equipment for measuring oxygen consumption, and allow the sample to be subjected to an undetermined added heat flux from the flames. Finally, prior art small-scale tests are unresponsive to the flames' own radiation and thus ignore an essential effect which controls the burning at large scale.
As a result, there is presently an inadequate correlation between the measurements derived from bench-scale flammability tests and actual flammability hazards on a large scale. Because bench-scale tests of the prior art fail to accurately indicate large-scale flammability, there is widespread mistrust of current standard flammability tests, and the art accordingly relies heavily on full-scale tests for flammability assessment. However, full-scale tests are very expensive, are difficult to reproduce, require such large samples that they cannot reasonably be considered for screening new materials under development and, since they are empirical, give little guidance for assessing hazards in related situations.
Thus, there is a need in the art for a bench-scale flammability test for measuring flammability properties of a sample of material, such that the measured properties are an accurate indication of the large-scale flammability properties of the material. The test should be compact and simple and free from the need for complicated equipment for chemical analysis. The present invention meets these objectives and other objectives which will become apparent from the following detailed description.